[leetcode] 112. Path Sum

Question:

Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.

For example:
Given the below binary tree and sum = 22,

              5             / \            4   8           /   / \          11  13  4         /  \      \        7    2      1

return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.

Solution:

简单的递归。如果是叶子则判断当前值是否等于要求的值，不是叶子就递归下去，把要求的值减去当前值成为下面要求的值。

/** * Definition for a binary tree node. * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    bool hasPathSum(TreeNode* root, int sum) {        if (!root) return false;        if (!root->left && !root->right && sum == root->val) return true;        return hasPathSum(root->left, sum-root->val) || hasPathSum(root->right, sum-root->val);    }};